2,179 research outputs found
<a> prismatic, <a> basal, and <c+a> slip strengths of commercially pure Zr by micro-cantilever tests
No full textSlip strengths of <a> basal, <a> prism, and <c+a> pyramidal systems in commercially pure zirconium have been determined using micro-cantilever testing. A range of single crystal cantilevers 0.5 µm to 10 µm wide, oriented for single slip were prepared using focused ion beam (FIB) machining and subsequently deflected using a nanoindenter. The critical resolved shear stress (Ïcrss) was found by fitting a crystal plasticity finite element model to the experimental load-displacement data for these micro-bending tests. All the three slip systems in alpha-Zr show a marked size effect in bending described well by CRSS(W)=Tau0 + AWn, where W is the cantilever width, Tau0 is the CRSS at the macro scale and n=-1. The exponent, n, of near -1 is in good accord with hardening caused by the back stress generated by dislocations piling up at a diffuse barrier caused by the reduction of stress near the neutral axis. The macro scale CRSS values were used to successfully simulate deformation of a conventional macroscopic compression test
PIN, BLACK ANGUS BEEF
No full textImage shows a souvenir pin from the 2002 Olympic Winter Games. The pin consists of an official Certified Angus Beef logo attached to the official Olympic logo, inside an elliptical, blue and black field
HR-EBSD Measurements near Twins in Zicaloy-2
No full textHR-EBSD measurements made on a Zircaloy-2 sample deformed to 2.7% in tension to generate multiple deformation twins.
HR-EBSD measurements were made using A Bruker HReFlash detector mounted on a Zeiss Merlin SEM. Sample preparation used Ar ion beam milling on a Gatan PECS II system as a final step.
The strain, stress and dislocation density variations available here were then calculated using in-house Matlab code (XEBSD) described in the following publications:
High resolution electron backscatter diffraction measurements of elastic strain variations in the presence of larger lattice rotations
TB Britton and AJ Wilkinson
Ultramicroscopy, (2012), vol. 114, 82-95
doi:10.1016/j.ultramic.2012.01.004
Measurement of residual elastic strain and lattice rotations with high resolution electron backscatter diffraction
TB Britton and AJ Wilkinson
Ultramicroscopy, (2011) vol. 111, 1395-1404
doi:10.1016/j.ultramic.2011.05.007
Determination of elastic strain fields and geometrically necessary dislocation distributions near nanoindents using electron back scatter diffraction
AJ Wilkinson and D Randman
Philosophical Magazine, (2010), vol. 90, 1159-1177
doi:10.1080/14786430903304145
Crystal Plasticity Analysis of Micro-Deformation, Lattice Rotation and Geometrically Necessary Dislocation Density
FPE Dunne, R Kiwanuka, AJ Wilkinson
Proc. Royal Society A, (2012), vol. 468, 2509-2531
doi:10.1098/rspa.2012.0050 Stress fields close to twin tips and the associated local neighbourhoods of a hexagonal close-packed (HCP) polycrystal were studied in details. For this purpose, a coarse grain textured Zircaloy-2 sample was firstly strained uniaxially in a macroscopic direction that favours tensile twin formation. The sample was then unloaded and residual elastic strains and lattice rotations measured using the high-resolution electron backscatter diffraction (HR-EBSD) technique. Measured elastic strain maps of various clusters of grains including parent and twin pairs were then analysed. Stress, dislocation density, and their associated concentrations close to twin tips, within twins, in the immediate neighbouring grain, at the intersection of two twins, and within parent grains were investigated. It is shown that the stress field at the twin tips varies as a function of local neighbourhood. High stress, lattice rotation, and dislocation density concentrations were generally observed close to twin tips both within twins and within the immediate neighbouring grains. It is shown dislocation density concentration is maximum at the intersection of two twins which can potentially provide susceptible site for crack nucleation
Autograph of Jimmy Elaine Wilkinson Meyer in "Any Friend of the Movement"
No full textThe title page and an autograph by the author, Jimmy Elaine Wilkinson Meyer, in their work ""Any Friend of the Movement: Networking for Birth Control 1920-1940"" with an inscription.Gloria- Kudos and thanks for your labors and inspiration. Looking to better days ahead. Jimmy Meye
Crystal Wilkinson: 48th Annual ODU Literary Festival
No full textCrystal Wilkinson, a recent recipient of a Writing Freedom fellowship, is the award-winning author of Praisesong for the Kitchen Ghosts, a national-bestselling culinary memoir, Perfect Black, a collection of poems, and three works of fiction—The Birds of Opulence, Water Street and Blackberries, Blackberries. She is the recipient of an NAACP Image Award for Outstanding Poetry, an O. Henry Prize, an Academy of American Poets Fellowship, a USA Artists Fellowship, and an Ernest J. Gaines Prize for Literary Excellence. She has received recognition from the Yaddo Foundation, Hedgebrook, The Vermont Studio Center for the Arts, The Hermitage Foundation and others. Her short stories, poems and essays have appeared in numerous journals and anthologies including most recently in The Atlantic, The Kenyon Review, STORY, Agni Literary Journal, Emergence, Oxford American and Southern Cultures. She was Poet Laureate of Kentucky from 2021 to 2023. She currently teaches creative writing at the University of Kentucky where she is a Bush-Holbrook Endowed Professor and Director of the Division of Creative Writing. Her memoir Heartsick is forthcoming from Crown
Crystal Wilkinson
No full textPublicity photo submitted by author/presenter for ODU\u27s Annual Literary Festival 2025.https://digitalcommons.odu.edu/litfest_images/1018/thumbnail.jp
Review of Mechanisms of strength and hardening in austenitic stainless 310S steel: Nanoindentation experiments and multiscale modeling
No full textThis Zenodo record is a permanently preserved version of a PREreview. You can view the complete PREreview at https://prereview.org/reviews/7371559.
A review of preprint arXiv:2205.03050 [v1] (https://doi.org/10.48550/arXiv.2205.03050)
"Mechanisms of strength and hardening in austenitic stainless 310S steel: Nanoindentation experiments and multiscale modeling"
F. J. Domínguez-Gutiérrez, K. Mulewska, A. Ustrzycka, R. Alvarez-Donado, A. Kosińska, W. Y. Huo, L. Kurpaska, I. Jozwik, S. Papanikolaou, and M. Alava
Reviewer: Angus J Wilkinson
27 November 2022
Overview
The paper presents interesting experimental and molecular dynamics (MD) simulation studies on nanoindention of a face centred cubic Fe-Ni-Cr stainless steel 310S. 310S is high in both Cr (~25wt%) and Ni (~20wt%) compared to other austenitic stainless-steel grades and finds application in areas where high temperature environmental degradation is a concern. A strength of the work is that the high quality of both the nanoindentation experiments and the MD simulations.
The nanoindentation experiments were undertaken with a Berkovich tip with loads in the range 0.25 to 10 mN, so that shallow indents below 200 nm depth resulted. Data for even the smallest <50nm, 0.25nM) indents appeared to be of good quality indicating careful experimentation on difficult measurements. Results from repeat tests are given to indicate noise levels and scatter in material response.
The MD simulations of the 310S alloy were undertaken using LAMMPS with an embedded-atom method (EAM) potential and models with Fe, Ni and Cr atoms in an initially randomised substitutional solid solution. In line with other literature a fixed layer furthest from the indented surface, and a thermostatic layer allowing for heat dissipation were included with the model which was initially equilibrated at 300 K. Given that repeat simulations were conducted for multiple orientations the models size was kept as large as reasonable possible and consisted of a total of 8.5-9 million atoms.
The most significant challenge for the work is in making a strong connection between the experiments and simulations when computational resource prohibits using a larger model, while experimental uncertainties are more marked for smaller indents. The dilemma is perhaps made most evident by comparing the 10 nm tip radius and 5 nm maximum indent depth used in the simulations with the smallest experimental indents of a little under 50 nm. A more fundamental barrier to direct comparison is that the simulations are for tip radius of 10 nm, while the experiments are for much larger value (~100 nm seems likely from load-displacement data though the actual value is not quoted). The larger tip radius in the experiments provides access to much larger indentation strains than is possible in the simulations, while larger strain gradients are in place for the simulations. Finally, there is a large difference in loading rate (and therefore deformation rate).
Reading the preprint provoked the following comments and questions some of which might be useful to the authors.
Main Points
· Given the challenges above in making direct comparisons the conclusion of excellent agreement between experiment and simulation should perhaps be softened, similarly the work itself does not deal with high temperature behaviour, or effects of irradiation so conclusions regarding the suitability of the alloy for nuclear applications seem out of scope.
· The attempt to estimate GND density is interesting, especially as the strain gradients are extremely high for the simulations, and quite a bit lower for the experiments. Typically, a length scale needs to be set in describing how the total dislocation density is split between GND and SSD densities, but this has not been made explicit here. For the MD simulations it may be that all dislocations have been taken to contribute to the GND density, but it is not clear what volume term has been used (text around eq 12-13 suggests contact diameter may be the indicative lengthscale). For the Ma-Clarke model how was the shear strain calculated (the Ma-Clarke paper was for Berkovich rather than spherical indents)? No details are given for the calculation of GND density from the EBSD map, but the characteristic lengthscale is likely markedly larger than for the MD simulation, and the effects of this should be discussed. A little more detail in methodologies should be given for all of this analysis. Fig 11 c) is the only figure where both simulation and experimental data are shown directly on the same plot. Ma & Clarke (and subsequently Nix & Gao) used both SSD and GND densities as contributions to a Taylor hardening expression to link strain gradients to indentation size effects. Have the authors thought of extended their analysis to see if this can consistently link the markedly lower hardness values seen for deeper experimental indents with the much higher hardness reported for MD simulations?
· Some interesting dislocation density-based laws are introduced in eq 8 to 10. These are fit to the MD simulation results for dislocation density in fig 8a. It would be good to state the dislocation mean free path and annihilation constants obtained. As with the point above can a Taylor hardening model then be used to connect to hardness values and then provide a link to the experimental data. [In passing the text describing eq 10 refers to grain size though perhaps indent size is more relevant here].
· Results from simulations and experiments show relatively little anisotropy in either indentation modulus or hardness (eg figs 4b, fig 5, fig 8b) – it seems odd then to state in the conclusions that "…310S indicates anisotropic properties…".
Minor Points
· Caption on fig 4 swaps parts (a) and (b)
· Scale bars should be added to fig 6, fig 7 a and b, fig 9, fig 11a and b, and fig 12
· Fig 9b – the 5nm and unload images seem to be identical though difference are talked about in the main text.
Angus J Wilkinson
27 November 202
HR-EBSD Measurements near Twins in Zicaloy-2
No full text<p>HR-EBSD measurements made on a Zircaloy-2 sample deformed to 2.7% in tension to generate multiple deformation twins. <br />
HR-EBSD measurements were made using A Bruker HReFlash detector mounted on a Zeiss Merlin SEM. Sample preparation used Ar ion beam milling on a Gatan PECS II system as a final step. <br />
The strain, stress and dislocation density variations available here were then calculated using in-house Matlab code (XEBSD). The work and further analysis of the results is described in</p>
<p><em>Assessment of residual stress fields at deformation twin tips and the surrounding environments</em>, Abdolvand & Wilkinson, Acta Materialia (2016)<br />
dx.doi.org/10.1016/j.actamat.2015.11.036</p>
<p> </p>
<p> </p>
<p>The analysis methods implement in XEBSD are described in the following publications:</p>
<p>High resolution electron backscatter diffraction measurements of elastic strain variations in the presence of larger lattice rotations <br />
TB Britton and AJ Wilkinson <br />
Ultramicroscopy, (2012), vol. 114, 82-95 <br />
doi:10.1016/j.ultramic.2012.01.004</p>
<p>Measurement of residual elastic strain and lattice rotations with high resolution electron backscatter diffraction <br />
TB Britton and AJ Wilkinson <br />
Ultramicroscopy, (2011) vol. 111, 1395-1404 <br />
doi:10.1016/j.ultramic.2011.05.007</p>
<p>Determination of elastic strain fields and geometrically necessary dislocation distributions near nanoindents using electron back scatter diffraction <br />
AJ Wilkinson and D Randman <br />
Philosophical Magazine, (2010), vol. 90, 1159-1177 <br />
doi:10.1080/14786430903304145</p>
<p>Crystal Plasticity Analysis of Micro-Deformation, Lattice Rotation and Geometrically Necessary Dislocation Density <br />
FPE Dunne, R Kiwanuka, AJ Wilkinson <br />
Proc. Royal Society A, (2012), vol. 468, 2509-2531 <br />
doi:10.1098/rspa.2012.0050</p>
Corrigendum to “A mechanistic study of the temperature dependence of the stress corrosion crack growth rate in SUS316 stainless steels exposed to pressurized water reactor primary water” [Acta Mater. 114 (2016) 15–24]
No full textThe authors regret that one of the main contributors to this paper was unintentionally omitted from the author list in the final version of the manuscript. The complete author list should read: Martina Meisnara, Arantxa Vilalta-Clementea, Michael Moodya, Angus J. Wilkinsona, Koji Ariokab, Sergio Lozano-Pereza,∗ The authors would like to apologise for any inconvenience caused
Height, health, and inequality: the distribution of adult heights in India
No full textThis paper explores the relationship between adult heights and the distribution of income across populations of individuals. There is a long literature that examines the relationship between mean adult heights and living standards. If adult height is set by the balance between food intake and charges to disease in early childhood, it is informative about economic and epidemiological conditions in childhood. Because taller populations are better-off, more productive, and live longer, the relationship between childhood conditions and adult height has become an important focus in the study of the relationship between health and wealth. Here I follow one of the tributaries of this main stream. A relationship between income and height at the individual level has implications for the effects of income inequality on the distribution of heights. These relationships parallel, but are somewhat more concrete than, the various relationships between income inequality and health that have been debated in the economic and epidemiological literatures, Richard G. Wilkinson (1996), Angus Deaton (2003).
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